1. Field of the Invention
The present invention relates to a polymer for a photosensitive resin composition used as a phosphor slurry for forming a phosphor layer of a color picture tube, and more particularly, to a polymer which can enhance adhesive strength of a photosensitive resin composition, to which a diazo-type photosensitive material as a nonchrome-type photosensitive material is added, so that a phosphor material can be stably attached on a surface of a panel.
2. Description of the Prior Art
Generally, a phosphor layer is formed on an inner surface of a panel for a color picture tube by (a) depositing a phosphor slurry consisting of a phosphor material and a photosensitive resin on the inner surface of the panel, (b) exposing the deposited slurry to a light and (c) cleaning out an exposed or unexposed portion of the deposited slurry. To fixedly form the phosphor layer on the panel, the phosphor slurry is not varied in its properties of matter while having an affinity for the panel and depositing properties.
As a conventional phosphor slurry, a phosphor suspension, which is made by suspending a phosphor material in a liquid made by mixing sodium dichromate as a photosensitive material with a polyvinyl alcohol aqueous solution as a polymer, has been used. However, since chrome contained in a waste sodium dichromate contaminates soil, alternative materials have been developed.
A polyvinyl alcohol-sodium dichromate type, a polyvinyl alcohol-sodium dichromate-diazo type, and a polyvinyl alcohol-azido type photosensitive material arc well-known as photosensitive resin compositions used for the phosphor slurry.
Among the photosensitive resin compositions, the polyvinyl alcohol-sodium dichromate type is mostly used as it is highly sensitive. However, when forming the phosphor layer using this composition, it is very difficult to adjust a width of dots.
In addition, when storing the polyvinyl alcohol-sodium dichromate type for a long time, a dark reaction occurs between a polyvinyl alcohol and a sodium dichromate, in which Cr.sup.+6 of the sodium dichromate is reduced into Cr.sup.+3 by an oxidation-reduction reaction. Particularly, the chrome contained in the waste sodium dichromate still contaminates the soil.
The polyvinyl alcohol-sodium dichromate-diazo type enhances sensitivity of the polyvinyl alcohol-sodium dichromate type, thereby reducing the light exposing time. However, it also contains the chrome which contaminates the soil.
The polyvinyl alcohol-azido type photosensitive material has good developing properties, but low adhesive strength, not stably attaching the phosphor material on the inner surface of the panel. Therefore, the polyvinyl alcohol-azido type photosensitive material is used only for forming a black matrix of the color picture tube.
In addition a diazo-type photosensitive material is well known as a nonchrome-type photosensitive material. However, this material has a drawback in that when mixed with a polyvinyl alcohol, the photosensitivity is quickly reduced.